Nanako, literally 'fish eggs' or 'fish roe' in Japanese, is a metalworking technique in which a surface is covered with tightly packed, uniformly sized circular punch marks. The result is a textured ground that resembles a field of fish roe — small domes packed in regular rows. Nanako is a traditional decorative finish in Japanese metalwork, used on sword fittings (tsuba, fuchigashira, kashira, menuki), inrō and netsuke fittings, and metal art objects. The technique has been a hallmark of Japanese craftsmanship for centuries and is documented in collections including the Victoria and Albert Museum, the British Museum, and the Tokyo National Museum.

Technique

The work is executed with a domed punch — the nanako-tagane — that is held vertically against the metal surface and struck with a small hammer. Each strike produces a single hemispherical impression. The smith works systematically across the surface in straight rows, advancing the punch by exactly one impression diameter between strikes. Maintaining uniform spacing and depth across hundreds or thousands of impressions requires extreme precision — any irregularity is immediately visible against the regular pattern.

The punch is sharpened and re-domed periodically as it wears. Different surface qualities are produced by varying punch diameter (from sub-millimetre for fine work to several millimetres for coarser grounds), strike force, and metal hardness. Some craftsmen use a graduated set of punches, working coarser toward the centre and finer toward the edges of a piece, or grading punch size to fit the geometry of an irregular form.

Use and contrast

Nanako is most often used as a textured ground that provides visual contrast to raised, inlaid, or engraved designs. A tsuba or fuchigashira will typically have a raised or inlaid main motif — a plant, animal, or figure — set against a nanako field. The texture catches and holds light differently from polished or chased surfaces, allowing the smith to control how an entire piece reads under different lighting conditions. The same approach is used in repoussé and engraved compositions on inrō, lacquer hardware, and decorative metal panels.

Materials

Nanako is most commonly executed in shakudo (a copper-gold alloy that patinates to a deep purple-black), shibuichi (a copper-silver alloy that patinates to grey-green), and pure copper. Silver and gold nanako are also worked, but the alloy patination of shakudo and shibuichi is part of what makes the texture read so strongly. The finished surface is patinated chemically to develop the characteristic Japanese alloy colours.

Modern use

Nanako remains in active use among contemporary metalsmiths working in traditional Japanese styles, in jewellery, sword-fittings restoration, and metal art. The technique is taught at the major Japanese craft schools and through apprenticeship traditions, and has been adopted by Western metalsmiths through the international study of Japanese metal arts. Nanako appears in modern jewellery as a textured ground on rings, pendants, and earrings made by smiths working with shakudo, shibuichi, and silver-copper compositions.

Further reading

• Victoria and Albert Museum — Japanese metalwork collections
• British Museum — Japanese sword fittings and metal art
• Metropolitan Museum of Art — Japanese decorative arts
• Ganoksin — Japanese metalsmithing techniques